[+] add function GetSubscriberByUser for the agenda-widget

storage/storage.go

@@ -13,6 +13,7 @@ type Storage interface {
 	AddSubscription(eventid string, subscription Subscription) error
 	UpdateSubscription(eventid string, subscriber string, deletesubscription Subscription) error
 	UpdateEvent(Event) error
+	GetSubscriptionByUser(subscriber string) ([]Subscription, error)
 }
 type StorageImpl struct {
 }